PMMA film: roll to roll nano-imprinted (center: heated for shape recovery)
​Structural coloring in 3D printing (TPU)
(FYP) Wong JC
(FYP) Sim Jayden
​Chameleon snake
FDM printed phone cases
(FYP) Yang HX
​(FYP) Sim Jayden
​FDM（熔融沉积成型）3D 打印的过程中，打印头通过熔融材料逐层沉积构建物体。而具有结构色的激光膜通常是通过微纳米结构来反射和干涉光线，从而产生颜色。要使得 FDM 3D 打印出的部件在其底部表面形成与激光膜上的微结构相对应的图案或微结构，主要涉及到以下几个关键问题：
  1. 激光膜的耐热性：FDM 3D 打印的过程中，打印材料是通过加热熔融的（通常在 180°C 到 250°C 之间）。激光膜必须能够在这个温度下保持稳定，才能在材料沉积时保持表面微结构。
  2. 材料与膜表面的相容性：打印材料（如 PLA、ABS）在熔融状态下与激光膜接触时需要良好的附着性，同时不能破坏膜的微结构。打印材料的表面张力和激光膜的表面性质（如粗糙度、润湿性）对最终效果有很大影响。
  3. 微结构的复制：FDM 打印的材料在冷却和固化过程中，是否能够充分复制激光膜的微纳米结构。这取决于材料的流动性、冷却速率，以及激光膜表面的微结构尺寸。如果微结构非常细微（纳米级），FDM 材料可能难以精确复制。
  4. 打印参数的控制：打印温度、速度、喷嘴与膜的接触压力等参数需要精确控制，确保打印材料能够填充激光膜的微结构并固化后保持该结构。
理论上，如果激光膜的微结构可以在高温下保持，并且材料在沉积时能够复制这些微结构，那么 FDM 打印出的部件底部可以具有与激光膜表面相对应的微结构。
In the FDM (Fused Deposition Modeling) 3D printing process, the print head builds the object layer by layer by depositing molten material. A laser film with structural color typically produces colors through micro- and nanoscale structures that reflect and interfere with light. To make the bottom surface of an FDM 3D printed part form a pattern or microstructure corresponding to the laser film’s microstructure, the following key issues must be considered:
  1. Heat resistance of the laser film: During the FDM 3D printing process, the material is melted at temperatures typically between 180°C and 250°C. The laser film must remain stable at this temperature to preserve its surface microstructure during material deposition.
  2. Compatibility between the material and the film surface: The printing material (such as PLA or ABS) must have good adhesion to the laser film while in a molten state, without damaging the microstructure of the film. The surface tension of the printing material and the surface properties of the laser film (such as roughness and wettability) significantly affect the final result.
  3. Replication of the microstructure: During the cooling and solidification process, the FDM material must be able to sufficiently replicate the micro- and nanostructures of the laser film. This depends on the material’s flow characteristics, cooling rate, and the size of the microstructure on the laser film. If the microstructure is extremely fine (on the nanoscale), it may be challenging for the FDM material to replicate it accurately.
  4. Control of printing parameters: Printing parameters such as temperature, speed, and the contact pressure between the nozzle and the film must be precisely controlled to ensure that the printing material fills the laser film’s microstructure and maintains that structure after solidification.
In theory, if the microstructure of the laser film can remain stable at high temperatures and the material can replicate the microstructure during deposition, the bottom of the FDM-printed part can exhibit microstructures corresponding to those on the laser film’s surface.
​​打印出的结构色，为什么肉眼看着不是很明显，而通过手机，可以看出绚丽的结构色？
这种现象可以归因于人眼和手机摄像头在感知光线和颜色上的差异，主要包括以下几个方面：
  1. 光谱敏感性差异：
    人眼的视网膜有三种感光细胞（视锥细胞），分别对红、绿、蓝光敏感，但对色彩的感知并不是对所有波长都同样敏感。结构色通常由微纳米级的周期性结构通过干涉、衍射等光学效应产生，对光线的入射角和观察角度非常敏感。肉眼在观察这些颜色时，可能由于照明条件、观察角度或者眼睛对光谱的敏感度不同，导致结构色不太明显。
    相比之下，手机摄像头的传感器通常对光的感知更均匀，尤其是手机相机的传感器可以在不同光照强度下自动调整曝光和对比度，从而使结构色更加显眼。
  2. 成像设备的光学增强：
    手机摄像头通常具有多个镜头和滤波器，能够捕捉更广的光谱范围，并通过算法增强图片中的颜色饱和度和对比度。这种算法在图像处理过程中，会放大微小的光学差异，增强了结构色的视觉效果。
  3. 反射与折射的动态处理：
    结构色的产生依赖于光线的反射、折射和干涉，而人眼的视角是固定的，当光线进入眼睛时，由于视角的限制，结构色可能不够明显。手机摄像头可以通过不同角度的光线捕捉，以及像素级的光线处理，动态调整图像中不同区域的亮度和色彩，呈现出肉眼难以察觉的结构色变化。
  4. 对比度和分辨率：
    人眼对低对比度的颜色（如淡色调或亮度相似的颜色）的分辨能力较差。而手机摄像头通过调节曝光和色彩对比度，可以放大这些细微的差异，使结构色更加显眼。
综上所述，手机摄像头借助先进的传感器、图像处理算法和光学设计，能够比人眼更灵敏地捕捉结构色，并且通过图像增强技术呈现出更为绚丽的效果。
Why are the structural colors on the printed object not very noticeable to the naked eye, but appear vibrant when viewed through a smartphone?
​This phenomenon can be attributed to the differences in how the human eye and smartphone cameras perceive light and color, primarily in the following aspects:
  1. Spectral sensitivity differences:
    The human eye has three types of cone cells in the retina, each sensitive to red, green, and blue light, but it is not equally sensitive to all wavelengths of light. Structural colors are often generated by micro- and nanoscale periodic structures through interference and diffraction effects, which are highly dependent on the angle of light incidence and observation. When viewed with the naked eye, structural colors may not be very prominent due to lighting conditions, viewing angles, or the eye's sensitivity to different parts of the light spectrum.
    In contrast, smartphone cameras usually capture light more uniformly. The sensors in smartphone cameras can automatically adjust exposure and contrast under different lighting conditions, making structural colors more visible.
  2. Optical enhancement by imaging devices:
    Smartphone cameras typically feature multiple lenses and filters, which can capture a wider range of the light spectrum and enhance color saturation and contrast through image processing algorithms. These algorithms can amplify subtle optical differences, making the structural colors more vivid.
  3. Dynamic processing of reflection and refraction:
    Structural colors are produced by light reflection, refraction, and interference. The human eye’s field of view is fixed, and due to this limitation, structural colors may not be very noticeable when light enters the eye. In contrast, smartphone cameras can capture light from different angles and dynamically adjust brightness and color across various regions of the image, revealing subtle changes in structural color that may go unnoticed by the naked eye.
  4. Contrast and resolution:
    The human eye has limited ability to distinguish between low-contrast colors, such as subtle shades or colors with similar brightness levels. Smartphone cameras, however, can adjust exposure and color contrast to amplify these fine differences, making structural colors stand out more clearly.
In summary, smartphone cameras, with their advanced sensors, image processing algorithms, and optical design, can capture structural colors more sensitively than the human eye. Through image enhancement technologies, they present the colors in a more vivid and striking way.

​Holographic Chocolate

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